Fast Cloud Adjustment to Aerosols

The goal of project S1 "Fast cloud adjustment to aerosols" is an improved understanding of the effect of anthropogenic pollution (aerosols) on clouds, radiation, precipitation and climate. Questions that need to be answered are

To what extend will changes in aerosols have an impact on clouds and precipitation?

Which are the most important variables to take into account to be able to quantify this based on measurements?

These are not easy questions, because there are competing effects: on one hand, drizzle formation rate by the autoconversion process may be delayed so the cloud lifetime might be affected, on the other hand smaller cloud droplets can lead to more supercooled water freezing at higher altitudes, resulting in an increased surface precipitation. Even a strong effect of CCN and IN load can directly relate to precipitation.

To this, dedicated simulations with the high-resolved HD(CP)² model are conceived, performed, and analysed. The model is enhanced by the representation of essential processes. Moreover, HD(CP)² observational data are used to evaluate and further improve the model, and to work towards a detection and attribution of anthropogenic changes in observations.

Anthropogenic aerosols have an impact on cloud formation, cloud properties and their life times. Comparing those indirect aerosol effects on clouds, or the clouds themselves, in simulations and observations is hampered by changes in cloudiness due to air traffic.

A prerequisite for realistically simulating the cloud adjustment to aerosol-radiation interactions is a realistic representation of aerosol radiative properties in the model. The aim of work package 3 are new time-varying 3D distributions of cloud condensation nuclei (CCN) and aerosol radiative properties, which will be used in dedicated simulations with the ICON_GCM (global circulation model) and the high-resolved HD(CP)² model to analyze the cloud adjustment effects.

Atmospheric aerosol particles influence cloud properties by acting as the seeds for cloud droplet and ice particle formation. Work package 4 uses the ICON_LEM to investigate how changes in the concentration of cloud condensing and ice nucleating particles affect the microphysical characteristics of mixed-phase clouds, which comprise both liquid droplets and ice particles.

The aerosol and CCN (cloud condensation nuclei) profiles derived from COSMO-MUSCAT as an input for ICON-LEM are evaluated using measurements from HD(CP)² supersites. Multiwavelength lidar is the main instrument for this purpose.

Cloud observations from polar-orbiting satellites are used to investigate the scale- and regime dependency of cloud-aerosol relationships. The observed and modelled spatial and temporal distributions of cloud properties are analyzed by, e.g., the construction of probability density functions, also stratified with respect to meteorological parameters.